FIG. 7 is a block diagram showing an example of a conventional infrared gas analyzer. As shown in the figure, infrared light rays emitted from an infrared light source 1 are divided into two infrared light components by a distribution cell 2 to thereby enter a reference cell 3, and a sample cell 4, respectively. A gas not containing a measuring target component, such as an inert gas, and so forth, is sealed in the reference cell 3. A sample gas is distributed into the sample cell 4. As a result, only one of the two infrared light components of the infrared light rays, after divided by the distribution cell 2, on the side of the sample cell 4, is subjected to absorption by the measuring target component, subsequently reaching a detector 5.
The detector 5 has two chambers consisting of a reference side chamber 51 for receiving the infrared light component from the reference cell 3, and a sample side chamber 52 for receiving the other infrared light component from the sample cell 4, and a flow sensor 53 for detecting gas flow is provided in a gas distribution path linking the two chambers with each other. Further, a gas containing the same component as the measuring target component is sealed in the detector 5, and upon the respective infrared light components from the reference cell 3, and the sample cell 4, falling on the detector 5, the measuring target component of the gas, as sealed, absorbs the infrared light component, whereupon the respective gases inside the reference side chamber 51 and the sample side chamber 52 undergo thermal expansion.
Since a reference gas inside the reference cell 3 does not contain the measuring target component, there occurs no absorption of the infrared light component passing through the reference cell 3 by the measuring target component, and if the measuring target component is contained in the sample gas inside the sample cell 4, portions of the infrared light component are absorbed, thereby resulting in a decease in quantity of the infrared light component, falling on the sample side chamber 52 of the detector 5, so that thermal expansion of the gas inside the reference side chamber 51 becomes larger than thermal expansion of the gas in the sample-side chamber 52. The infrared light rays are interrupted by a rotary sector 6, the rotary sector 6 repeating blockage and irradiation, and when the infrared light rays are cut off, the infrared light component falls on neither the reference side chamber 51 nor the sample side chamber 52, so that the gases do not expand.
Consequently, there occurs a pressure difference according to the concentration of the measuring target component of the sample gas, periodically between the reference side chamber 51 and the sample side chamber 52, thereby causing the gases to come and go through the gas distribution path provided between both the chambers. Behavior of the gases is detected by the flow sensor 53 to be subsequently amplified at an AC voltage by a signal processing circuit 7, thereby outputting a signal corresponding to the concentration of measuring target component. Reference numeral 8 denotes a synchronous motor for driving the rotary sector 6, and 9 a trimmer for adjusting balance between the infrared light components falling on the reference cell 3, and the sample cell 4, respectively.
Thus, if the concentration of the measuring target component of the sample gas undergoes a change, there occurs a change in quantity of the infrared light component falling on the detector 5 (the sample side chamber 52), so that it is possible to obtain an output signal corresponding to the concentration of the measuring target component via the signal processing circuit 7.
With the conventional infrared gas analyzer as shown in FIG. 7, for the infrared light source 1, use is made of a ceramic heater, and so forth, with a configuration for overcoming various problems, such as poor thermal responsiveness at the light source, fluctuation, drift, and so on, of the light source.
That is, while the rotary sector is in use for turning the infrared light rays ON/OFF, the infrared light rays emitted from a common light source are divided into the two infrared light components before falling on the sample cell and the reference cell, respectively, in order to eliminate effects of light source variation.
FIG. 8 is a block diagram showing an example of an infrared light source excellent in thermal responsiveness. FIG. 8A is a plan view, and FIG. 8B is a sectional view taken on line A-A in FIG. 8A. As shown in the figures, an infrared light source 1 is structured such that a filament 12 in a micro-bridge-like shape is supported above a recess 11 formed in a silicon substrate 10.
The filament 12 has its plane shape formed by forming a polycrystalline silicon layer 14 highly doped with boron on top of a silicon dioxide film 13 formed on a silicon substrate 10, and subsequently, by applying linear patterning to the polycrystalline silicon layer 14.
Then, a portion of the silicon substrate 10, below the filament 12, is removed by anisotropic differential concentration etching using the silicon dioxide film 13 formed on both the top and bottom faces of the silicon substrate 10, respectively, as masks, thereby forming the recess 11, whereupon there is implemented a micro-bridge structure for supporting the filament 12 linear in shape, above the recess 11.
Subsequently, portions of a silicon dioxide film 15 formed on the polycrystalline silicon layer 14 are removed to form electrodes 16a, 16b, and current is supplied to the filament 12 via the electrodes 16a, 16b, thereby causing the filament 12 to generate heat to emit infrared rays corresponding to a heat generation temperature.
The infrared light source 1 as described is excellent in thermal responsiveness and high in emissivity of the infrared rays while ON/OFF thereof at high speed is possible, thereby being driven with a simple drive circuit. Further, as a semiconductor process is utilized in manufacturing the same, it is possible to manufacture high-performance infrared light sources having uniform properties at a low cost on a mass production basis.    [Patent Document 1] JP-A No. 131230/2002    [Patent Document 2] JP-B No. 3174069    [Patent Document 3] JP-A No. 221737/2001